There is no single best cat food for all cats,  nor is it a good idea to just feed them one type. Try to avoid any artificial colors or chemical preservatives and the main ingredient definitely needs to be meat of some kind, not grain. Other than that, see what they like. 

Rotate flavors and brands because each of them has a slightly different mix of vitamins, minerals, and ingredients. Rotating means that you get a good balance overall. 

Think of it this way - you can fix yourself the healthiest meal you can think but if you eat exactly the same meal all the time you are going to end up with too much of some nutrients and not enough of others. 

Variety is key to a healthy diet for any person or animal.  

Canned food can be great for maintaining a healthy weight and it's ideal to have part or an all canned food diet, particularly with a male cat. With that said, the majority of cats do well on a kibble diet.